1. Field of the Invention
The present invention relates to butterfly valves. The present invention also relates to intake air control devices that have butterfly valves and are used for internal combustion engines.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 2001-74156 teaches a known butterfly valve. This butterfly valve has a throttle shaft that is a one piece member integrated with a valve body by an insertion molding process. Therefore, during the molding process, the flowability of a molten resin for molding the valve body around the throttle shaft may be low, and therefore, the quality of the butterfly valve may be degraded in some cases. Thus, when the molten resin injected into a molding die flows in a diametrical direction with respect to the throttle shaft, the molten resin may impinge on the throttle shaft so as to be diverged into two streams in different directions, which streams flow about the throttle shaft by a distance corresponding to half the circumferential length of the throttle shaft for filling the space around the throttle shaft with the molten resin. Therefore, in the region on the backside of the throttle shaft with respect to the direction of flow of the molten resin toward the throttle shaft, a cavity blank or a weld line may be formed to cause improper molding. As a result, the quality of the throttle valve may be degraded.
Therefore, there is a need in the art for a butterfly valve that is improved in quality. Also, there is a need in the art for an intake air control device having a butterfly valve that is improved in quality.